1. Field of the Invention
This invention relates to a method of producing multilayered metal effect lacquerings with improved weather-resistance in which metal effect lacquer coats are treated with a selected top coat lacquer, and to sheets having such multilayered lacquer finishes.
2. Description of the Prior Art
Multilayered lacquer finishes built up of several lacquer layers are used, for example, for lacquering motor vehicles. The coat of clear lacquer forming the last, outermost layer of the multilayered lacquering is generally stoved in. It is obtained from clear lacquers which generally contain poly(meth)acrylates or copolymers thereof as film-formers. They are obtained by copolymerization of (meth)acrylic acid esters of monohydric alcohols with (meth)acrylic acid esters which still contain functional hydroxyl groups and which may also contain as copolymer component other comonomers such as styrene, vinyl toluene, vinyl esters and small proportions of monomers containing carboxyl groups. These acrylate resins are used, for example, in combination with polyisocyanates in organic solvents.
Other clear lacquers contain alkyd resins in addition to the polyacrylate resins. These alkyd resins are synthesized from phthalic acid and polyols which are modified with various fatty acids or other monocarboxylic acids and may also be hardened in combination with polyisocyanates (Temple C. Pattan, Alkyd Resin Technology, Interscience Publishers, John Wiley & Sons, New York, London, 1962; Wagner-Sarx, Lackkunstharze, 4th Edition, Karl Hanser Verlag, Munich, 1959; Ullmanns Encyclopadie der technischen Chemie, Vol. 14, pages 80-106, 1963).
These known clear lacquers are distinguished by the hardness and elasticity thereof. When used as top coat lacquers in a multilayered lacquering in which the last layer contains metal pigments, in other words for a metal effect lacquering, the known clear lacquers tend to form cracks on exposure to weathering and UV light such as occurs in sunny regions. Clear lacquers obtained from acrylate resins also tend to become matt after weathering and exposure to UV light in weathering tests, and this renders the metallic effect unsightly.
It is an object of the present invention to provide new clear lacquers which are suitable for use as top coat lacquers for multilayered metal effect lacquerings, show no tendency to form cracks and impart improved weather-resistance to the lacquer finishes.
This problem may be solved according to the present invention by using, for the production of multilayered metal effect lacquerings, clear lacquers, the binders of which have the composition described in more detail below.